In a small mixing bowl, combine the radish, onion and carrot with the lime juice and 1 tablespoon olive oil. Season with sea salt and pepper, to taste; and set aside.
Heat 1 tablespoon oil and garlic in a pan. When garlic starts to sizzle, about 30 seconds, add mushrooms and sliced peppers. Sauté for 4 to 5 minutes, turning until lightly browned. Season with sea salt, to taste.
Set a large pan over medium-low heat. Arrange 2-3 tortillas in a single layer. Flip them after 30 seconds or so. As they come off the stove, wrap them in a clean tea towel. Repeat with a second batch. Fill each taco with black beans, if using, and mushroom pepper mixture. Garnish with the slaw, cilantro and another squeeze of lime, if desired. Repeat with the remaining tortillas.