Chop tomatoes into 6-8 wedges each, slice cucumber into thick half-moons, dice bell pepper into large squares, and slice red onion into thin rings. If the onion tastes too sharp, rinse slices under cold water for 30 seconds and pat dry.
Pit and halve Kalamata olives by pressing each olive with the side of a knife to split it and removing the pit, or use pre-pitted olives.
Cut block feta into ½-inch cubes or break into large chunks by hand to keep texture substantial.
Combine tomatoes, cucumber, bell pepper, onion, olives, and feta in a large bowl. Do not toss yet.
Just before serving, drizzle olive oil and red wine vinegar over the vegetables. Sprinkle dried oregano and sea salt, then toss gently to coat. Let salad rest 10 minutes for flavors to meld before tasting and adjusting salt if needed.