Tempeh is a vegetarian protein that crumbles easily; here it stands in for ground meat in this tempeh taco recipe.
Combine tomatoes, cilantro, minced onion, jalapeño, 1 Tbsp. lime juice, and 1/4 tsp. salt in a medium bowl. Set aside.
Whisk yogurt, lime zest, 1/8 tsp. salt, and the remaining 1 Tbsp. lime juice in a small bowl. Set aside.
Heat oil in a large nonstick skillet over medium heat. Add diced onion; cook, stirring often, until softened, 3 to 4 minutes. Add garlic; cook for 1 minute. Add mushrooms and tempeh; cook until the mushrooms are softened, about 5 minutes. Stir in chili powder, cumin, and the remaining 1/4 tsp. salt; cook for 1 minute more.
To serve: Divide the tempeh mixture among taco shells. Top with the salsa fresco, lime yogurt sauce, and cheese.
To make ahead: Prepare salsa (Step 1) and yogurt sauce (Step 2) and refrigerate separately for up to 1 day.