One Tray Baked Halloumi

• 800 g chickpeas, drained, rinsed
• 500 g cherry tomatoes, halved
• 1 red onion, finely sliced
• 360 g halloumi, thinly sliced
• 2 tbsp harissa paste
• 0.25 cup pumpkin seeds (pepitas)
• 200 g baby spinach leaves
• 1 lemon