Cut the zucchini in half lengthwise and trim the ends. Use a spoon to scoop out the seeds, creating boats.
Arrange the zucchini halves cut-side up in a 9x13-inch baking dish. Drizzle with the olive oil and bake for 12–15 minutes, or until they begin to soften.
Meanwhile, heat a large skillet over medium-high heat. Add the ground beef and diced onion and cook for 4–5 minutes, breaking the beef into crumbles, until browned. Drain any excess grease.
Stir in the minced garlic and cook for 1 minute until fragrant.
Add the taco seasoning, salt, pepper, and salsa. Stir until well combined and heated through.
Spoon the beef mixture evenly into the partially baked zucchini boats.
Sprinkle the shredded Mexican cheese over the top.
Return the baking dish to the oven and bake for 5 minutes, or until the cheese is melted.
Garnish with chopped fresh cilantro and diced Roma tomato before serving.