Step 1Preheat oven to 180°C and line a large baking tray with baking paper.
Step 2Heat oil in a large non-stick frying pan over a medium heat. Sauté onion for 3 minutes, or until softened. Add sweet potato and cook, stirring, for 3–4 minutes, or until softened. Add garlic, lemon zest and chilli flakes and cook, stirring, for 1 minute, or until fragrant. Add kale and cook, stirring, until just wilted. Set aside until cool.
Step 3Combine kale mixture, seeds, ricotta and egg in a large bowl; season well with cracked black pepper. Place mushrooms cut side up on the prepared tray. Divide ricotta mixture between mushrooms, cover with foil and roast for 15 minutes. Remove the foil and roast for a further 10 minutes, or until mushrooms are just tender and golden.
Step 4Serve stuffed mushrooms with the steamed broccolini.