Preheat the oven to 200°C.
Stuff the thyme into the sea bass cavity.
Whisk egg whites to soft peaks and fold in the salt.
Spread a third of the mixture on a lined tray, add fish, and cover with remaining mixture.
Bake for 30 to 35 minutes until the crust is crisp.
Crack the crust, remove the skin from the fish, and place on a plate.
Blanch runner beans in boiling water for 2 minutes then refresh in iced water.
Combine runner beans, parsley, shallots, broad beans, lettuce, and croutons in a bowl.
Whisk mustard, vinegar, lemon juice, oil, sugar, and seasoning to make the dressing.
Toss the salad with the dressing and serve alongside the sea bass.