Shares of Zscaler (ZS -1.49%) ended last week with a bang. The cloud security stock rocketed nearly 30% on the heels of its strong fiscal fourth-quarter results. 

However, despite that big move higher, Zscaler's stock is still nearly 50% below its 52-week high. That makes it looks like a screaming buy, given the explosive growth it's delivering and sees ahead. 

Blistering growth

Zscaler's unstoppable growth was on full display during its fiscal fourth quarter. The cybersecurity company's revenue exploded 61% in the period, growing to $318.1 million. That pushed its full-year revenue up 62% to nearly $1.1 billion. 

Revenue has been growing at a 55% compound annual rate since 2018. It accelerated to more than 60% last year, up from 56% year-over-year growth in its 2021 fiscal year and 42% in its 2020 fiscal year.

Meanwhile, the company is becoming increasingly profitable. While it's not producing GAAP earnings, it's delivering improving non-GAAP earnings and growing free cash flow. Non-GAAP net income jumped 33.8% last year to $101.3 million, while Zscaler's free cash flow jumped 61% to $231.2 million, putting it at 21% of its revenue. 

Just scratching the surface of its growth prospects

Zscaler expects to continue growing rapidly. The cybersecurity company sees revenue rising to as much as $1.5 billion in its 2023 fiscal year, a 37.5% increase. While that's a deceleration from recent years, it's still an impressive pace. Meanwhile, it sees non-GAAP net income surging over 70% to a range of $173 million to $176 million. 

The cloud security company envisions its revenue rising to $5 billion in the coming years. That's still only a fraction of the $72 billion serviceable market opportunity for its current slate of security products. 

The company has several growth drivers. Adding new customers is a big one. It ended its fiscal year with over 6,700 total customers, up 20% year over year. 

Another driver is its expanding relationship with existing customers. Zscaler sees more than a sixfold upsell opportunity for its two core security products with existing customers. Meanwhile, the company continues to invest in innovation to expand its product portfolio. Emerging products contributed 14% of its new business last year, which it expects will continue in fiscal 2023.

The company shortens the time to market for innovations and expands its market opportunity by making highly targeted early stage acquisitions. For example, in 2021, Zscaler bought Smokescreen Technologies, a deception technology leader. The company integrated that deception technology into its platform, helping drive additional growth last quarter. 

Zscaler has the financial resources to continue investing in innovation. The company ended its fiscal year with over $1.7 billion in cash -- a $228.8 million increase from the prior year -- against only $968 million of debt in the form of convertible senior notes. That strong balance sheet is a huge competitive advantage in the current environment. Higher interest rates and lower stock prices make it harder for companies to obtain capital at attractive rates to fund growth. With a cash-rich balance sheet and a business generating free cash flow, Zscaler has the funds to invest so that it can continue growing at a rapid rate.

Rapidly growing into its valuation

With shares down almost 50%, Zscaler is trading at a much more attractive valuation these days, given its explosive growth. Its price-to-sales ratio has tumbled from over 60 times to around 27 times and is down to 17 times on a forward basis. While that's not cheap, it's much more reasonable, especially for a company with Zscaler's growth potential. Add in its significant financial flexibility, and it looks like a screaming buy for patient investors with a long-term mindset.