Preheat the oven to 400 degrees. Slice the zucchini into 1/2-inch rounds. Core, seed, and remove the white ribs from the poblano, then thinly slice. Place the tortillas on a baking sheet and bake for about 4 minutes, until crispy. Set aside.

Toss the zucchini and poblano on the same baking sheet with a drizzle of olive oil and a pinch of salt and pepper. Place in the oven for about 20 minutes, tossing halfway through cooking, until tender and golden brown.

Meanwhile, halve, pit, and dice the avocado. Halve, peel, and finely dice 1/4 cup red onion. Core, seed, and dice the tomato. Halve the lime.

Make the tomato-avocado salsa: Toss the tomato, onion (to taste), and avocado in a medium bowl with a drizzle of olive oil, a squeeze of lime, and a pinch of salt and pepper.

In a small pot, heat the black beans and their liquid over medium-low heat, stirring occasionally. Once warmed through, mash with a fork until fairly smooth. Season with salt and pepper.

Make the tostadas: spread the mashed black beans onto the crispy tortillas. Top with the mozzarella and roasted vegetables. Place on a baking sheet and bake for about 5 minutes, until the cheese has melted.

Top the tostadas with the tomato-avocado salsa and a dollop of sour cream. Finish with a squeeze of lime, if desired. Enjoy!