Pea feta summer herb frittata

Name: Pea, feta & summer herb frittata
Ingredients: 300g new potato (such as Jersey Royals), halved if large; 4 egg and 2 egg whites; splash of milk; 1 garlic clove, crushed; 1 tbsp gluten-free wholegrain mustard; handful mixed soft herbs, such as dill, mint and parsley, roughly chopped; 3 tbsp cream cheese; 1 tbsp olive oil; 1 courgette, coarsely grated; ½ tsp chilli flakes; 140g petits pois (defrosted if frozen); 100g feta cheese, crumbled; 50g sundried tomato, drained and roughly chopped; 100g bag salad leaves, to serve