
Preheat oven to 400 degrees F. Lightly oil a 9 x 13 baking dish or coat with nonstick spray.
Cut each zucchini in half horizontally, then carefully scoop out the center of the zucchini, reserving for another use, leaving about 1/2-inch of zucchini on the skin.
Heat canola oil in a large cast iron skillet over medium high heat. Add ground beef and cook until browned, about 3-5 minutes, making sure to crumble the beef as it cooks; drain excess fat.
Add onion, and cook, stirring frequently, until translucent, about 2-3 minutes. Stir in garlic until fragrant, about 1 minute.
Stir in diced tomatoes & green chilies and taco seasoning until thickened and flavors have blended, about 2-3 minutes. Stir in cilantro.
Place zucchini in a single layer, skin-side down, onto the prepared baking dish; season with salt and pepper, to taste. Add beef mixture to each zucchini.
Place into oven and bake until the zucchini is tender, about 20-25 minutes. Sprinkle with cheddar cheese during the last 5 minutes of cooking time.
Serve immediately.