Cook pasta according to directions on the package.
Meanwhile, heat 1 tablespoon of the oil in a large skillet over medium-high heat. Add the onion slivers to the skillet and sauté until transparent (about 5 minutes), stirring occasionally. Add the minced garlic; sauté 2 more minutes, stirring frequently. Push onion-garlic mixture to one side of the skillet.
Add the remaining tablespoon of oil to the skillet. Add the shrimp; sauté until transparent (about 4 -6 minutes), turning halfway through cooking. Transfer shrimp to a medium bowl and set aside.
Add tomatoes, tomato paste, pepper flakes, salt, and sugar if desired, to skillet. Simmer 10-15 minutes, stirring occasionally. Return shrimp to sauce; stir to combine. Remove from heat.
Top pasta with sauce. Sprinkle with cheese and top with basil as desired.