Financial technology, or fintech, has been growing explosively over the past few years and is showing no signs of slowing down. Here's why three of our contributors think Green Dot (NYSE: GDOT), Interactive Brokers (NYSEMKT: IBKR), and Visa (NYSE: V) may be worth a look right now.Matt Frankel, CFP (Green Dot): One fintech stock on my radar is Green Dot.Green Dot is known primarily as the market leader in prepaid debit cards, pioneering that space almost two decades ago, but there's a lot more to the company.