Bring the water to a boil in a medium pot. Whisk in the instant polenta along with half the salt. Reduce heat to low and stir for 3 to 5 minutes until thick and creamy. Remove from heat and cover to keep warm.
Heat the olive oil in a large skillet over medium heat. Add the minced garlic and cook for 30 seconds until fragrant.
Add the halved cherry tomatoes to the skillet. Cook for 3 to 4 minutes, stirring occasionally, until they begin to soften and release juices.
Add the shrimp, remaining salt, and black pepper. Cook for 3 to 4 minutes, stirring often, until the shrimp turn pink and opaque.
Stir the pesto into the skillet and cook for 1 minute more to warm through and coat the shrimp and tomatoes.
Spoon the polenta into bowls. Top each portion with the shrimp and tomato mixture. Sprinkle with Parmesan cheese and fresh basil leaves before serving.