Prepare the Chicken. Season the chicken breasts with salt, pepper, and a pinch of chili powder. In a large skillet, heat a bit of cooking oil over medium-high heat. Cook the chicken breasts until they're nicely browned and cooked through (usually about 5-7 minutes per side, depending on the thickness). Remove them from the skillet and set them aside.
Cook the Vegetables and Pasta. In the same skillet, add a bit more oil if needed. Sauté the diced onions and minced garlic until they're tender and fragrant. While the aromatics are cooking, prepare the pasta according to the package instructions until it's al dente. Drain and set it aside.
Make the Sauce. In a large pot, combine the Rotel diced tomatoes and green chilies, heavy cream, chicken broth, cumin, and a pinch of chili powder. Cook over medium heat until the mixture is heated through, stirring occasionally.
Combine Everything. Slice the cooked chicken into bite-sized pieces. Add the cooked pasta, sliced chicken, and sautéed onions and garlic to the pot with the sauce. Mix everything together until it's well combined.
Add Cheese. Stir in the shredded cheddar cheese until it's fully melted and the sauce becomes creamy and cheesy. Season with salt and pepper to taste. Feel free to adjust the spices according to your preference.
Serve and Garnish. Once everything is mixed and heated through, serve your Chicken Spaghetti With Rotel in bowls. If desired, garnish with parmesan cheese and chopped fresh cilantro or parsley to add a pop of color and freshness to the dish.