The biggest problem with vegetarian lasagna is that it can be very watery. You can replace part of your pasta with thin slices of zuchini or eggplant, but dry them very well or even put them in the oven for awhile to dehydrate. Spinach needs to be not just drained, but squeezed. Your tomato sauce should be quite thick. It's been ages since I've done one, so don't have a recipe, but remember to get the vegetables you layer as dry as possible or you wind up with a watery mess. The no-boil noodles are great because they absorb some of the water given off by the vegetables.