Open mackerel sandwich with fennel slaw

INGREDIENTS

• 2 long slices rye bread
• 4 tbsp soft cheese
• 2 fillets hot smoked peppered mackerel (about 150g/5½oz), skinned and flaked
• 1 fennel bulb , cored and thinly sliced
• ½ small red onion , thinly sliced
• 2 tsp small capers
• 1 lemon , ½ juiced, ½ wedges
• 1 tbsp extra-virgin olive oil
• small bunch chives , snipped