Dressing: Spread tomatoes on a baking sheet and cook under a preheated grill of oven for about 15 minutes or until blackened (flip them each 5 minutes). Let cool. Dice the tomatoes, put in a strainer that is on a bowl and let drain for 5 minutes to keep the juice. In the bowl, add oil, vinegar, garlic, salt, pepper and red pepper flakes. Mix until homogeneous. Add the tomatoes and stir. (You can do this mixture ahead of time, cover it and it can be good in fridge up to 2 days. Before using, bring to room temperature).
Pasta: In a skillet, heat oil at medium-high heat. Add shrimps, salt and pepper. Cook for about 3 minutes or until pink. Add dressing and stir to coat well.
Meanwhile, in a large saucepan, in salted boiling water, cook pasta for about 10 minutes or until al dente. Drain pasta and put back in the saucepan. Add the shrimp mixture and spinach. Set aside 1/4 cup feta cheese, add remaining feta to the pasta and stir to coat well. When ready to serve, sprinkle with the feta you set aside (1/4 cup).