Place ingredients in a food processor or blender with a pinch of salt.
Blend until smooth, then strain into a jug. Cover and set aside to rest for 30 minutes at room temperature.
Dip a piece of paper towel in melted butter and use to brush base of a 16cm non-stick crepe pan or frypan over medium heat. When hot, pour in just enough batter to cover the base. Tilt pan so batter covers base in a thin film and pour any excess back into the jug. Cook crepe for about 1 minute until underside is golden, then use a metal spatula to flip. Cook other side for just under a minute until golden.
Transfer to a plate and cover with foil to keep warm. Repeat for remaining crepe mixture, stacking crepes on the plate as you go.
Preheat oven with rack in middle position.
Heat 1 tablespoon oil in a large pot over medium-high heat. When oil shimmers, add onions. Add zucchini and capsicum, a few handfuls at a time, and cook, stirring frequently. Add cans of cannellini beans and the cans of diced tomatoes. Remove from heat add nutmeg, salt, and black pepper. Cover surface with plastic wrap.
Layer crepes, vegetables sauce and spinach in a baking dish. Top with crepes. Repeat with a second layer of crepes, and mix of vegetables.
Dollop over ricotta cheese followed by parmesan.
Cover with foil and bake 45 minutes. Remove foil and continue baking until cheese is golden in places and lasagne is bubbling along the edges, about 15 minutes.
Remove lasagne from oven and let stand 20 minutes before slicing and serving.