Remove the skins of the grilled peppers and onion, then slice them thinly.
Lightly whisk the eggs in a small bowl. Add the dill, then season with salt and pepper.
Heat 1 Tbsp of olive oil in a non-stick, oven-proof frying pan. Once hot, add the sliced vegetables. Cook for a minute or so to warm through then pour over the egg mixture, letting it spread out evenly around the pepper and onion slices. Crumble the feta all over the top. Put a lid on and cook for about 6 minutes.
Meanwhile turn on the grill in your oven.
When the top is almost set put the pan in the oven and brown the top - this should take a couple of minutes.
Slide the frittata onto a plate - let it cool a bit or completely, depending on how you want to serve it.
Cut it into wedges if you want it as a meal, or cut it into cubes and serve as nibbles (at parties, picnics etc).