Espresso Chili Marinated Steak Tostadas

Name: Espresso Chili Marinated Steak Tostadas
Ingredients: 2 cloves garlic; Kosher salt and freshly ground black pepper; 1/4 cup double shot brewed espresso, at room temperature; 2 tablespoons Mexican chili powder blend; 2 tablespoons vegetable oil, plus more for brushing; 1 1/2 pounds skirt steak; 1 medium red onion, cut into 1/2-inch thick rings kept intact; Vegetable oil, for frying; 8 white corn tortillas; Kosher salt; 1 avocado, thinly sliced; 1 jalapeno, sliced (seeds removed for less heat); 5 ounces Cotija cheese (about 1 cup); 1/2 cup Mexican crema or sour cream; 1 cup fresh cilantro leaves; 2 limes, cut into wedges