Cook spaghetti according to package directions, drain and set aside -OR- **If you're good at multi-tasking, you can cook the spaghetti noodles and the shrimp at the same time and they should both be done at the same time.
Sprinkle blackening seasoning evenly over shrimp and set aside.
Coat a large, non-stick skillet with cooking spray and add oil. Place over medium-high heat until hot.
Add shrimp to skillet; cook 2 minutes on each side or until shrimp turn pink.
Stir in lemon juice, tomatoes and pepper. Turn heat down to simmer and cook until thoroughly heated.
Spoon shrimp mixture over drained pasta and serve immediately.