Preheat oven to 350 F.
Prepare peppers by slicing off the tops a 1/4 inch thick. Clean out peppers and set aside with their tops (don’t discard).
Slice off the top of the zucchinis, a 1/4-inch thick. Cut the zucchini in three equal parts and save the top. Hollow out the zucchini to make room for the stuffing. Leave a 1/4 inch rim of zucchini. Finely chop the inside, and set the zucchini aside.
Peel onion and cut off bottom and top. With a paring knife make a slice along the side of the onion lengthwise, right through to the centre. Carefully peel 5 layers, ensuring you keep the onion layers intact. Finely chop remaining onion and add to bowl with zucchini.
In a large deep sauté pan, heat oil over medium heat. Add onions, the zucchini insides and sauté for 1-2 minutes or until soft and translucent.
Add, cumin, salt, ground pepper and sauté for an additional minute.
Add in ground lamb and cook until browned, about 5-6 minutes.
Add spinach and sauté until slightly wilted.
Turn off heat and stir in mint, lemon, rice and tomato puree.
Stuff all the vegetables with the rice and meat mixture and arrange in a baking dish large enough to fit all the vegetables snug.
Dilute the bouillon and tomato paste in the warm water and pour on top of all the stuffed vegetables. Place tops on peppers and zucchinis. Drizzle with the olive oil and season with salt and pepper.
Cover baking dish tightly with foil and bake in preheated oven for 50-60 minutes until vegetables are soft and tender. The baking time will depend on how large your vegetables are. Remove foil from baking dish and increase oven to 400ºF. Continue baking for 20-25 minutes until tomatoes and peppers have charred and softened.
Turn off oven, re-cover baking dish with foil and let stand for 15 minutes in warm oven. Transfer to a serving platter and drizzle with pan juices.