First, preheat your oven to 350 degrees Fahrenheit. Lightly grease a 9 x 13 baking dish and set aside.
Next, in a large pot, add 3 quarts of water. Stir in a generous pinch of salt and pepper. Add the chicken breasts and bring the pot to a VERY low boil on medium-high heat.
Cook the chicken gently until it is no longer pink in the center. Remove from the water and let cool. Using two forks, shred the chicken. Set aside.
Bring the cooking water to a boil. Add the dry pasta and cook to package directions for al dente (about 9 minutes). Drain, reserving about 2 cups of the pasta water.
Reduce the stove top to low. In the same pot (now drained and empty), combine the Rotel, soups, cubed Velveeta, hot sauce, onion powder + chili powder.
Cook and stir until the cheese mixture is smooth. Remove from heat and fold in the prepared chicken and spaghetti. Add the milk and 1 ½ cups of the reserved pasta water (more as needed).
Transfer the mixture to the prepared baking dish. Sprinkle the cheddar cheese over the top.