I cheated a bit with this sandwich. I didn't bother with the onions, I stuck some pickled red cabbage on top instead. It was massively flavourful though and i loved the peas and pesto.
Turkey Smashed Pea and Pesto Sandwich (from The Sweets Life)
1/4 small red onion, sliced
2 tbsp white wine vinegar
2 tbsp butter
200g frozen peas
salt and pepper
4 tbsp pesto
200g turkey pieces
8 slices bread, toasted
Place the onion slices and vinegar in a small bowl and allow to sit for 3-5 mins, until onion is tender and bright pink.
Meanwhile, heat butter in a frying pan over medium heat. Add the peas and salt and pepper. Cook for 5-7 mins, until the peas are heated through. Mash until peas hold together.
Spread pesto on four of the sandwich slices, then top with the peas, onion, and turkey. Finish with remaining slices of bread. Serve.