Adjust rack to top position (top and middle positions for 4 servings) and preheat oven to 450 degrees. Wash and dry produce.

Halve, peel, and thinly slice onion; mince a few slices until you have 2 TBSP (4 TBSP for 4). Dice tomato. Roughly chop cilantro. Quarter lime. Halve, core, and thinly slice green pepper into strips. Drain and rinse beans.

In a small bowl, combine minced onion, tomato, half the cilantro, and a squeeze of lime juice. Season with salt and pepper.

In a separate small bowl, combine sour cream with a squeeze of lime juice. Season with salt and pepper. Stir in water 1 tsp at a time until mixture reaches a drizzling consistency.

Heat a drizzle of oil in a large pan over medium-high heat. Add green pepper, sliced onion, and half the Southwest Spice Blend (you’ll use the rest in the next step). Cook, stirring occasionally, until lightly charred and softened, 5-7 minutes. Season with salt and pepper. Turn off heat; transfer to a plate.

Heat pan used for veggies over medium-high heat. Add beans, Tex-Mex paste, remaining Southwest Spice Blend, and ¼ cup water (⅓ cup for 4 servings). Bring to a simmer and cook, stirring occasionally, until liquid has mostly evaporated, 3-4 minutes.

Remove from heat; gently mash beans with a potato masher or back of a spoon. Stir in 1 TBSP butter (2 TBSP for 4) until melted. (TIP: If mixture is too thick, stir in a splash of water.) Season with salt and pepper.

Drizzle tortillas with 1 TBSP olive oil (2 TBSP for 4 servings); brush or rub to coat all over. Arrange on a baking sheet in a single layer (divide between 2 sheets for 4). Gently prick each tortilla in a few places with a fork.

Bake on top rack, flipping halfway through, until lightly golden, 4-5 minutes per side. (For 4, bake on top and middle racks; flipping tortillas and swapping rack positions halfway through.) TIP: Watch carefully to avoid burning.

Once tortillas are toasted, remove sheet from oven. Carefully spread each tortilla with smashed beans, then top with veggies and Mexican cheese blend.

Return to top rack until cheese melts, 2-3 minutes.

Divide tostadas between plates. Top with pico de gallo, lime crema, and remaining cilantro. Serve with remaining lime wedges on the side.