Add the diced sweet potatoes to a microwave-safe bowl with 2 tablespoons of water. Cover the bowl with a plate or damp paper towel and microwave on high for 3 to 4 minutes until the potatoes are just tender when pierced with a fork. Drain any remaining water and set the bowl aside.
Warm the olive oil in a large skillet (10 to 12 inches) over medium heat. Add the diced onion and cook for about 3 minutes, stirring occasionally, until the onion softens and becomes translucent.
Add the ground beef to the skillet with the onion. Use a wooden spoon to break the beef into small crumbles as it cooks. Continue cooking for 6 to 7 minutes, stirring now and then, until the beef is browned and no pink remains. If there's a lot of grease in the pan, carefully drain it off.
Stir in the minced garlic, tex mex seasoning, ground cumin, salt, and pepper. Cook for about 30 seconds, stirring constantly, until the garlic becomes fragrant and the spices are toasted.
Add the pre-cooked sweet potatoes and salsa to the skillet. Stir everything together well. Let the mixture simmer uncovered for 5 to 7 minutes, stirring occasionally, until the sweet potatoes are fully tender and the sauce has thickened slightly.
Sprinkle the shredded cheddar cheese evenly over the top of the skillet. Cover the skillet with a lid and let it sit for 2 minutes so the cheese melts completely.
Remove the skillet from the heat. Top with fresh cilantro and serve immediately with lime wedges on the side.