Bake the tostadas

• Preheat the oven to 200 °C on convection (or 220 °C regular bake).
• Drizzle the avocado oil on a large baking sheet and rub both sides of each tortilla in the oil, then sprinkle with salt.
• Bake for 6 min on the first side, flip, and bake 3–5 more min until deep golden brown and crispy. Leave the oven on and set the tostadas aside to cool.

Cook the onion and spices

• In a medium skillet over medium heat, melt the butter, then add the diced onion.
• Cook until softened, 3–5 min, then stir in the garlic, chili powder, cumin and salt and cook 1 min.

Simmer the beans

• Add the pinto beans, a portion of the green salsa and the water.
• Bring to a simmer, then reduce the heat to medium-low and simmer uncovered for 7–10 min, stirring often and mashing the beans with the spatula, until thickened and the liquid has reduced.
• Remove from the heat.

Bake the salsa and cheese layer

• Pour the remaining green salsa on a quarter sheet pan and top with the shredded Mexican blend cheese in an even layer.
• Bake for 8–10 min until the cheese is melted and bubbling, then broil for 1–2 min at the end until extra golden brown.

Assemble and serve

• Spread a layer of warm beans over each tostada.
• Top with shredded lettuce, chopped onion and cilantro.
• Use a spatula to separate a section of melted cheese about the size of a tostada, lift and slide it on top. Serve immediately with lime wedges.