Cook grits according to package directions. Stir in cubed cheese and cayenne pepper. Keep warm over low heat.
Heat butter and olive oil in a large skillet over medium-high heat. Sauté garlic and tomato in hot butter-oil mixture until tomato begins to soften. Stir in shrimp and lemon juice. Sauté until shrimp are bright pink on the outside and the meat is opaque. Season with salt.
Spread warm grits on a serving platter and cover with shrimp mixture.