Step 1: Heat a large, deep skillet or Dutch oven over medium-high heat. Add 1 tablespoon of olive oil. Once shimmering, add 1 pound of lean ground beef. Break it up with a spoon and cook until browned, about 5-7 minutes. Drain any excess grease.
Step 2: Add 1 chopped yellow onion and 2 minced garlic cloves to the skillet with the cooked ground beef. Sauté for 3-5 minutes, until the onion softens and becomes translucent and the garlic is fragrant.
Step 3: Stir in 1 packet (1 ounce) of taco seasoning mix and 1 teaspoon of chili powder. Cook for 1 minute, stirring constantly, to toast the spices and release their aroma.
Step 4: Pour in 1 (15 ounce) can of tomato sauce, 1 (10 ounce) can of Rotel (diced tomatoes with green chilies, undrained), and 2 cups of chicken broth. Bring the mixture to a simmer, stirring occasionally.
Step 5: Break 12 ounces of spaghetti noodles into 2-3 inch pieces and add them to the simmering sauce. Push the spaghetti down into the liquid to ensure it's fully submerged. If needed, add an extra splash of broth or water to cover the noodles.
Step 6: Reduce the heat to medium-low, cover the skillet, and cook for 15-20 minutes, or until the spaghetti is al dente and most of the liquid has been absorbed. Stir frequently, about every 3-4 minutes, to prevent the pasta from sticking to the bottom and ensure even cooking.
Step 7: Remove the lid. Stir in 1 cup of shredded cheddar cheese and 1 cup of shredded Monterey Jack cheese (or a Tex-Mex blend) until melted and fully incorporated.
Step 8: Top the taco spaghetti with the remaining 1 cup of shredded cheese. Cover the skillet again for 2-3 minutes, or until the cheese is beautifully melted and bubbly.
Step 9: Remove from heat. Garnish with fresh cilantro, a dollop of sour cream, and sliced jalapeños if desired. Serve immediately and enjoy!