Step 1 Preheat oven to 200°C. Mix garlic, thyme and lemon juice in a small bowl. Put mushrooms on a large baking tray. Spray with a light coating of cooking oil and drizzle lemon mixture on top. Bake for 40 minutes, or until mushrooms are cooked.
Step 2 Meanwhile, place beans, stock and lemon zest in a deep bowl. Purée with a stick blender (or in a food processor) until just smooth.
Step 3 Rinse quinoa well and place in a large saucepan with 2 cups cold water; bring to the boil. Reduce heat to low; cover and simmer for 12–15 minutes, or until all water evaporates.
Step 4 Combine quinoa, corn and peas in a large bowl; microwave for 2–3 minutes, or until hot. Heat bean purée in a small saucepan set over medium heat for 3–5 minutes, or until hot.
Step 5 Place mushrooms on plates, top with quinoa mix and bean purée and serve.