Step 1 Preheat oven to 180°C. Pour stock into a medium saucepan, bring to the boil and keep warm. Heat half of the olive oil in a large saucepan set over medium–high heat. Add chopped onion and half of the garlic; cook, stirring, for 5 minutes, or until soft.
Step 2 Add rice and stir to coat. Add reserved stock, tuna and tomato; stir to combine. Transfer rice mixture to a large shallow baking dish, cover with a piece of foil and bake for 20 minutes.
Step 3 Remove baking dish from oven. Uncover foil and stir in peas. Bake for 10 more minutes, or until rice has absorbed most of the liquid. Stir in lemon juice.
Step 4 Meanwhile, bring a separate large saucepan of water to the boil. Cook broccoli for 5 minutes, or until just tender; drain and return to pan with remaining oil and garlic; toss to coat. Serve risotto with broccoli florets.