Salmon + Asparagus Quiche with a Side Salad

• 1 sheet shortcrust pastry, defrosted
• 415 g tin salmon, drained
• 1 bunch asparagus, ends removed and cut into 2inch pieces
• .5 red onion, thinly sliced
• 4 eggs
• .5 cup milk
• 2 cup mixed leaves
• 1 Lebanese cucumber, diced
• 200 g cherry tomatoes, halved
• 1 tbsp balsamic vinegar