Make the almond ricotta: Drain soaked almonds and place in a blender or food processor with 1/4 cup of the reserved soaking water; pulse until the texture is lumpy and resembles ricotta, adding more soaking water as needed.
Transfer the almond mixture to a clean container and stir in the probiotic powder until evenly distributed; cover with a clean towel and secure, then leave in a warm spot to ferment for at least 8 hours (10 hours if you prefer more tang).
When fermentation is complete, stir in 1 tablespoon olive oil, salt to taste, the grated garlic (if using), and nutritional yeast (if using); seal and refrigerate the almond ricotta until ready to use.
Make the spinach-walnut pesto: Toast the walnut halves in a dry skillet over medium heat until fragrant and lightly browned, about 3–5 minutes, then transfer to the blender or food processor.
Add the pesto garlic, lemon zest, lemon juice, packed spinach, 3 tablespoons olive oil, and salt and pepper to the walnuts; pulse until uniformly chopped, then blend briefly on high to form a chunky puree, scraping down the sides as needed.
Heat a 10–11-inch deep skillet over medium and add 1 tablespoon olive oil; sauté the diced onion, carrot, and zucchini until the onion is translucent and carrots are tender, about 4–5 minutes.
Add the cooked lentils, 2 minced garlic cloves, chili flakes, and salt and pepper; cook, stirring, until the garlic is fragrant, about 30 seconds.
Pour in the 3 cups (24 oz) tomato sauce and bring the mixture to a simmer.
Nestle the broken oven-ready lasagna noodles into the simmering sauce, pushing them down so they are mostly submerged; cover the skillet and gently simmer until the noodles are just tender, about 15–17 minutes, adding up to 1/4 cup water if the skillet seems to be drying out.
Stir the vegetables and noodles to ensure all noodles are softened. Dollop the almond ricotta and spoonfuls of spinach-walnut pesto over the top, using the back of a spoon to press the dollops into the layers; scatter a small handful of extra spinach if desired.
Cover and cook the lasagna for another 10 minutes to heat through and meld flavors, then serve hot.