In a large skillet, heat 2tbsp olive oil and toss in the chopped bread cubes. Cook on low heat, stirring frequently, until the bread is nicely toasted on all sides.
Combine chopped peppers, cucumber, onion, tomato and olives in a large bowl.
In a small bowl, whisk all the ingredients for the dressing until well combined.
Add the dressing, bread cubes and feta cheese (if using) to the veggies. Toss to combine. Set aside for 20~30 minutes for the flavors to mingle. Serve at room temperature.