Cook the pasta according to package directions.
Meanwhile, heat the olive oil in a large nonstick skillet on medium-high heat. Add onions and cook and stir until translucent. Add in the garlic and stir until fragrant. Add in 1/2 cup of the dressing and cherry tomatoes and cook for about 5-6 minutes, stirring occasionally.
As the tomatoes cook and soften, smash them with the back of a wooden spoon. Continue to cook until the tomatoes make a chunky style sauce. (About 4-6 minutes) Add in the salt and pepper.
Drain the pasta and toss with the tomato mixture.
Add in the fresh basil. Season with additional salt and pepper if desired. Add remaining 1/4 cup of the dressing here and toss everything together. Add in the mozzarella cheese, chopped basil, and red pepper flakes if desired.