Chicken Tostadas

Name: Chicken Tostadas
Ingredients: 8 corn tostada shells; 1/4 cup extra-virgin olive oil; 1 small yellow onion, chopped; 2 (15-ounce) cans black beans, drained and rinsed; 3/4 cup water; 1/2 teaspoon ground cumin; 1/2 teaspoon garlic powder; 1/2 teaspoon kosher salt; 1/2 teaspoon dried oregano; 1/4 teaspoon black pepper; 2 cups shredded rotisserie chicken; 2 tablespoons salsa macha, plus more for drizzling; Shredded cabbage, sliced radishes, sliced avocado, pickled red onion, and crumbled queso fresco, for topping; Lime wedges, for serving