Place a skillet over medium heat. Add the olive oil, red onion, garlic and chili flakes. Cook for 2 minutes until the onion is soft. Add the spinach and cover with a lid. Cook for 2-3 minutes until the spinach is wilted.
Turn the heat to medium-high. Pour in the cherry tomatoes and bring to a simmer.
Add the shrimp and cook, stirring occasionally for about 6-8 minutes until the shrimp has cooked through.
Season with salt and pepper to taste. Scatter the feta cheese over the top and serve.