Spiced beef couscous

Ingredients

• 1 medium red onion, finely chopped
• cooking oil spray
• 450 gram beef mince
• 2 teaspoon ground cumin
• 2 teaspoon ground coriander
• 1 teaspoon ground turmeric
• 2 clove garlic, crushed
• 1 420g can corn kernels, drained
• 1 400g can red kidney beans, rinsed
• 3/4 cup couscous
• 40 gram butter, chopped
• 2 medium tomatoes, coarsely chopped
• 1 avocado, finely chopped
• lemon wedges, to serve
• 3/4 cup (180ml) boiling water