Spray a large deep skillet with nonstick cooking spray and heat over medium.
Add the finely diced onion, minced garlic, and ground turkey to the skillet; season with salt and pepper and cook, breaking the turkey apart, until no longer pink.
Stir in the taco seasoning, the can of Rotel (including juices), the chicken stock, and the broken spaghetti pieces.
Cover the skillet, bring to a boil, then reduce heat and simmer until the spaghetti is softened but still slightly firm, about 7 minutes.
While pasta simmers, whisk together the evaporated milk and flour until smooth.
When spaghetti is al dente, stir the milk-flour mixture into the skillet and cook, stirring, until the sauce thickens slightly.
Remove from heat and stir in the grated cheese, corn, and chopped green onions until cheese melts and ingredients are combined.
Divide into four portions and serve warm.