Wash and dry all produce. Preheat the oven to 400 degrees. Halve, peel, and finely dice the onion. Core, seed, and finely dice the bell pepper. Drain and rinse the black beans. Roughly chop the cilantro leaves and stems. Roughly chop the oregano leaves, then discard the stems. Halve the lime.

Heat a drizzle of oil in a large pan over medium heat. Add half the red onion, half the bell pepper, and cook, tossing for 4-5 minutes, until softened. Stir in the diced tomatoes, oregano, half the black beans, and 1/2 teaspoon sugar. Season generously with salt and pepper. Reduce the heat to low.

In a medium bowl, combine the remaining black beans, remaining bell pepper, half the cilantro, and as much red onion as you like. Stir in the juice of half a lime and a drizzle of oil. Season with salt and pepper.

Toast the tortillas: Place the tortillas on a baking sheet and place in the oven for 3-5 minutes, until slightly crispy. Stir the remaining cilantro (reserving a pinch for the guacamole) into the tomato ragu.

Halve, pit, and scoop the avocado flesh into a small bowl. Add a squeeze of lime juice and a pinch of cilantro. Mash with a fork until smooth. Season to taste with salt and pepper.

Assemble: Start assembling the Mexican tortilla stacks in this order: tortilla, tomato ragu, black bean salsa, and guacamole. Repeat to make a second layer. Any leftover fillings can be enjoyed on the side. Enjoy!