Coat a large saute pan with olive oil. Add 2 cloves garlic and a pinch crushed red pepper and bring to a high heat. When the garlic is golden brown and very aromatic, remove it from the pan and discard. Add the shrimp to the pan, sprinkle with salt and saute until the shrimp have turned pink and opaque, 3 to 4 minutes. Remove from the heat and cool. When the shrimp have cooled, cut them in half lengthwise and reserve.
Toss together the tomatoes, feta, cucumbers and onions. Smash and finely chop the remaining 2 cloves garlic and add it to the veggies. Add the oregano and a pinch of crushed red pepper. Add in the shrimp and toss to combine. Dress the salad with the vinegar and olive oil and season with salt. Let sit for at least 30 minutes before eating.