Preheat the oven to 400 degrees F. In a medium saucepan, heat 1 tablespoon olive oil over medium high. Dice the onion, then add it and the salt and cook 2 minutes, until just beginning to soften. Add the black beans and 1/4 cup salsa and stir to coat with the oil and onions. Cook, stirring periodically, until heated through, about 4 minutes. Mash and set aside. Meanwhile, spread the tortillas in a single layer on a baking sheet, then place in the oven until crisp, about 6 minutes, flipping the tortillas once half way through. Prepare any desired toppings. To serve, spoon the black beans over the crisp tortillas, then pile on the toppings. Enjoy immediately.