Heat 3 T. olive oil in saute’ pan.
Add the bread cubes and sprinkle with salt; cook over low to medium heat, tossing frequently, for 5-10 minutes until nicely browned. Add more olive oil as needed.
Place cucumber, red and yellow peppers, tomatoes and red onion in a large bowl.
For the vinaigrette, whisk together the garlic, oregano, mustard, vinegar, salt and pepper in a small bowl. While still whisking, add the olive oil until completely blended. Pour over the vegetables.
Add the feta, olives and bread cubes and mix together lightly. Set aside for 30 minutes for the flavors to blend. Serve at room temperature.