In a small pot, combine rice, ¾ cup water (1½ cups for 4 servings), and a pinch of salt. Bring to a boil, then cover and reduce to a low simmer. Cook until rice is tender, 15-18 minutes. Keep covered off heat until ready to use. 

While rice cooks, adjust rack to top position and preheat oven to 450 degrees. Wash and dry produce.

Trim and thinly slice scallions, separating whites from greens. Halve tomatoes lengthwise; using a spoon, scoop out tomato insides onto a cutting board. Roughly chop tomato insides and transfer to a medium bowl. Drain and rinse beans.

Heat a drizzle of oil in a large pan over medium-high heat. Add scallion whites, tomato insides, beans, a pinch of salt, and pepper. Cook, stirring occasionally, until scallion whites are tender and beans are warmed through, 2-3 minutes. 

Add Tex-Mex paste and ¼ cup water (½ cup for 4 servings). Bring to a boil, then reduce heat to low. Simmer until liquid has slightly reduced, 30-60 seconds.

Remove pan from heat.

Fluff rice with a fork; transfer to pan with bean mixture and stir to combine. Taste and season with salt and pepper.

Coat an 8-by-8-inch baking dish (9-by-13-inch baking dish for 4 servings) with a drizzle of olive oil. Fill each tomato half with as much filling as will fit; place tomato halves, cut sides up, in baking dish. Evenly sprinkle with Mexican cheese blend. TIP: Save any extra filling for serving.

Bake on top rack until tomatoes are tender and cheese melts, 8-10 minutes.

Divide stuffed tomatoes between plates and top with sour cream and scallion greens. Serve with tortilla chips and any remaining filling on the side. TIP: If you like things extra spicy, drizzle tomatoes with your favorite hot sauce.