Preheat your oven to 200°C/Fan 180°C/Gas 6. Drain and rinse the cannellini beans and shake them dry. Tip them into a bowl and mash till all the beans have broken up and are beginning to form a paste. Chop the mushrooms as finely as possible and add to the bowl.
Peel and grate 1 garlic clove into the bowl. Zest in the lemon. Finely chop the rosemary leaves and add those too. Tip in the breadcrumbs and 2 tsp ground cumin. Add 1 tbsp olive oil and plenty of seasoning. Using your hands, mix everything till the falafel mixture comes together.
Shape into 15-18 ping-pong sized falafel balls. Place them on a baking tray lined with baking paper. Slide into the oven for 30 mins, rolling them over half way through cooking.
While the falafel cook, make your spiced tomato sauce. Peel and finely chop the onion. Peel and grate the remaining garlic. Halve the chilli and flick out most of the seeds. Finely chop it.
Place a pan on a medium heat for 2 mins. When warm, drizzle in ½ tbsp olive oil and add the onion.Gently cook for 8 mins till softened. Add the garlic and chilli and stir together for 1 min. Pour in the chopped tomatoes. Add plenty of seasoning and bring to a simmer, covered, for 10 mins.
Meanwhile, finely chop the rainbow chard stems. Roughly shred the leaves. Juice half the lemon. Wrap the tortillas in foil.
When the falafels and tomato sauce have 5 mins left to cook, pop the foil tortilla package into the oven. Place a frying pan or wok on a high heat. Pour in ½ tbsp oil and add the chard stems. Cook for 2 mins. Then add the leaves and half the lemon juice with a good pinch of salt. Fry for 2 mins.
Carefully unwrap the tortillas and place a couple on each plate. Dollop on a spoonful of the tomato sauce and add a little chard. Top with the falafels. Serve with the remaining lemon, cut into wedges, for squeezing over.