Wash and dry produce.

Finely dice tomato. Trim and finely dice radishes. Trim and thinly slice scallions, separating whites from greens. Roughly chop cilantro. Core, deseed, and dice green pepper into ½-inch pieces. Drain and rinse beans. Trim and discard root end from lettuce; separate leaves.

In a medium bowl, combine tomato, radishes, scallion greens, half the cilantro, and 1 tsp vinegar (2 tsp for 4 servings). (Reserve remaining vinegar for another use.) Season generously with salt and pepper.

Heat 1 TBSP butter (2 TBSP for 4 servings) in a large pan over medium-high heat. Add green pepper, scallion whites, and a big pinch of salt. Cook, stirring occasionally, until softened, 3-4 minutes.

Stir in beans, Tex-Mex paste, and 2 TBSP water (4 TBSP for 4). Cook until beans are warmed through and water has absorbed, 2-3 minutes.

Stir in Mexican cheese blend until melted (save the Monterey Jack for serving).

Divide lettuce leaves between plates. Fill with bean filling. Top with salsa, sour cream, guacamole, Monterey Jack, and remaining cilantro. Serve.