It takes just 15 minutes to prep this fast vegetarian lasagna. Slideshow: More Lasagna Recipes
Preheat the oven to 425°. In a medium frying pan, heat the vegetable oil over medium high heat. Add the onion and cook for 5 minutes, until it is soft and starting to brown. Add the carrot, bell pepper and garlic and cook for 5 minutes. Stir in the marinara sauce and water.
In a medium bowl, whisk together the ricotta, egg, cream cheese, Dijon mustard, sea salt and freshly ground pepper.
In an 8-inch-square baking dish, spread 1/3 cup of the marinara sauce and top with 4 lasagna noodles, overlapping them a little. Pour half of the remaining marinara sauce over the noodles and cover with half of the ricotta. Arrange the rest of the noodles on top, and cover with the remaining marinara sauce and ricotta. Top with the Parmigiano-Reggiano cheese and cover the baking dish with aluminum foil.
Bake for 20 minutes then remove the foil and bake for 15 minutes, until the noodles are soft and the lasagna is bubbling and hot. Remove from the oven and let it sit for 10 minutes before serving.