1. Heat the olive oil in a large frying pan and add the sliced onions. Fry until soft and starting to caramelise, about 10 mins. Meanwhile, bring a large pan of water to the boil and add the green vegetables. Simmer for a couple of minutes until just cooked through, but still retaining some bite. Drain.
2. Add the garlic to the frying pan and cook for a further 2 mins. Remove half the mixture to a large bowl then add the green veg and spinach to the pan. Stir until the spinach has just wilted, then set aside. Add the peppers and most of the tomatoes (save one handful for later) to the bowl with the remaining onion and toss to combine.
3. In a large bowl, whisk together the egg and milk with plenty of seasoning. Heat a small, 20 cm/ 8 inch, frying pan with a little non stick cooking spray or butter. Pour in a thin layer of the egg mixture and top with a sprinkling of the green veg and spinach then scatter over a little of the crumbled feta. Cook for 3-5 mins until the omelette is cooked through and the feta is starting to melt. Set aside to cool. Repeat until you have used up about half of the egg mixture, about 5 omelettes. Repeat the same procedure using the pepper and tomato mixture, using mozzarella instead of feta.
4. To assemble the omelette stack, mix the ricotta with the herbs and plenty of seasoning. Spread on top of one of the green omelettes, then top with one of the red pepper ones and more of the ricotta mixture. Repeat, alternating flavours, until you have a large stack. Top with the rocket, remaining plum tomatoes, pine nuts and a drizzle of pesto.