Xoriatiki Salata (Country-Style Greek Salad)

Ingredients

• 4 plum tomatoes, cored and cut into 8 wedges
• 1 medium cucumber, halved lengthwise and cut crosswise into ½"-thick slices
• 1⁄4 medium red onion, thinly sliced
• 1⁄3 cup extra-virgin olive oil, plus more for drizzling
• 1 1⁄2 tbsp. red wine vinegar
• 1 tbsp. dried oregano, preferably Greek
• Kosher salt
• freshly ground black pepper
• 3 oz. feta cheese, crumbled