Cook grits according to package directions. Stir in cubed cheese and cayenne pepper. Keep warm over low heat.
Heat butter and oil in a large skillet over medium-high heat. Saute garlic and tomato until tomato begins to soften. Stir in shrimp and lemon juice. Saute until shrimp are pink. Season with salt to taste.
Spread warm grits on a serving platter and pour shrimp mixture on top.