Recipe is from Dating Vegans: Recipes for Relationships  by Anne Dinshah. This book is available from AVS and can be ordered here.

Excellent source of all B vitamins, even B12– from fortified nutritional yeast  
B vitamins support cellular energy production. B12  also supports DNA synthesis, blood cell formation and nervous system function. B12  supplements or B12  fortified foods are important for vegan diets.  
Yield: 8 servings  
3 cans (15 oz. each) great northern beans, drained (about 4½ cups)  
2 Tbs nutritional yeast  
1 Tbs olive oil  
2 tsp Italian seasoning  
1 tsp turmeric  
1 large can (28 oz.) tomato sauce (about 3 cups)  
8 oz. (1 small bunch) fresh spinach, or thawed frozen  
8 sheets whole wheat lasagna  
8 oz. white button or Portobello mushrooms, chopped

Preheat the oven to 350° F. Lightly oil a 9×13-inch casserole pan.  
Pour the beans into a large bowl and mash them a masher or fork. Add the yeast, oil, Italian seasonings, and turmeric to the beans and mix. Set the bean mixture aside.  
Wash the spinach in warm water to help it begin to wilt. Drain all the water from the spinach and chop it. Cover the bottom of the pan with ½ cup of the tomato sauce and half of the spinach. Put 4 pieces of pasta on the spinach. Spread ½ cup more tomato sauce on the pasta.  
Spread half of the mushrooms on the sauce. Add the remaining spinach and pack down lightly. 
Gently spread half of the bean mixture evenly over the spinach, which will help condense the spinach. Put the remaining 4 pieces of the pasta on the beans. Spread the remaining mushrooms and beans on the top of the pasta. Top with the remaining 2 cups of sauce, spreading evenly to completely cover the beans, mushrooms and pasta. Bake uncovered for 1 hour or until pasta is tender to a fork.  
Note: the pan should be full but not overflow as the sauce cooks. The spinach will condense as it cooks. If the pan is so full that the sauce might bubble over, place a baking sheet under the pan.  
Nutritional Information:430 Kcal, carbohydrates: 75 g, protein: 24 g, fat: 5 g.