Pour in the tomatoes and bring to a boil. Reduce the heat to medium and simmer, stirring occasionally, until the tomatoes are slightly thickened, 2 to 3 minutes. Add the shrimp and beans and cook, stirring occasionally, until the shrimp just start to turn orange, 2 to 3 minutes. Stir in the spinach and continue cooking, stirring occasionally, until the spinach is just wilted and bright green, and the shrimp are cooked through and opaque, 2 to 3 minutes. Remove the skillet from the heat and sprinkle the feta over top. Cover until the cheese is warmed through, 2 to 3 minutes. Serve immediately.