Boil the lasagna noodle sheets according to package directions. Drain when al dente and let cool. I like to toss with a little olive oil so they don't stick together.
Preheat the oven to 400 degrees(F).
In a large non-stick skillet, large enough to hold four cups of liquid, heat the olive oil on medium high.
Add the garlic, mushrooms, carrots and broccolini. Saute, reducing heat as needed until the carrots have softened. About 5-6 minutes. Push all the veggies to one side of the skillet.
Add the frozen spinach and peas to the empty side of the skillet and sauté until they start to heat and break apart. Then toss with the rest of the veggies.
Season all the veggies with a few pinches of salt and pepper and 2 teaspoons of the lemon juice. Continue to sauté for a few more minutes until the veggies are all cooked through.
Remove the veggies from the skillet and put in a separate bowl. Set aside.
In the same skillet, heat the vegan butter on medium. Once the butter has melted, add the flour and whisk together to form a roux. Simmer for another minute.
Pour the non-dairy milk into the skillet and whisk until fully combined. Making sure there are no lumps of roux left. Bring to a simmer, and reduce heat to medium low. Allow to simmer until the mixture thickens. About 2-4 minutes.
Season with a few pinches of salt and pepper, plus the remaining 2 teaspoons of lemon juice. Taste and adjust seasonings.
Add the veggies back to the skillet with the cream sauce and stir to combine. Remove from the heat.
In a 9x13 inch baking dish, add a little bit of the veggie cream sauce to the bottom of the dish and spread it out evenly.
Then place a layer of the lasagna sheets on top. Then 1/3 of the ricotta on top of the noodles, spreading it out evenly. Then 1/3 of the veggie cream sauce, spread it out. Then 1/3 of the mozzarella and 1/3 of the parmesan, sprinkling evenly.
Repeat with two more layers, noodles, ricotta, sauce, cheeses. (See video)
Cover with foil and bake for 45 minutes. Uncover and bake for 15 more minutes. Broil for a few minutes to brown the top if desired.
Let cool for a few minutes, cut into squares and serve topped with more lemon juice and red pepper flakes if desired.