1. Make the tostadas: Preheat the oven to 400F on convection (or 425F regular bake). Drizzle the olive oil on a large baking sheet. Rub both sides of each tortilla in the oil and sprinkle with salt. Bake for 6 mins on the first side, flip, and bake for 3-5 more mins until deep golden brown and crispy. Set aside to cool.
2. Make the beans: In a medium skillet over medium heat, melt the butter, then add the onion. Cook until softened, 3-5 mins, then stir in the garlic, chili powder, cumin, and salt. Cook for 1 min.
3. Add the pinto beans, green salsa, and water. Bring to a simmer, then reduce the heat to medium-low and simmer uncovered for 5-7 mins, stirring often and mashing the beans with your spatula, until thickened and the liquid has reduced. Remove from the heat.
4. Spread a layer of warm beans over each tostada. Top with shredded lettuce, onion, tomato, cheese, and salsa or taco sauce. Serve immediately and enjoy!
