Taco Mac and Cheese

12 oz whole wheat spiral pasta
1 lb hamburger
2 small onions, chopped
1 TBS flour
1 TBS butter
2 c milk
2 c Mexican-blend shredded cheese
1 pkg taco seasoning
1 can Rotel

Cook pasta according to package directions. Drain and set aside. Meanwhile, brown hamburger with onion. When browned, remove from skillet with slotted spoon, leaving the drippings. Set aside meat/onion. Add butter and flour to skillet; whisk together. Let bubble 1 minute. Whisk in milk. Stir constantly for 8-10 minutes or until slightly thickened. Remove from heat. Stir in cheese. Add hamburger mix, taco seasoning, and drained Rotel to the sauce. Toss with pasta and serve immediately.