Preheat oven to 375 degrees. Grease a 9-by-13 inch baking dish with olive oil.
Boil lasagna noodles in salted water until "al dente", being sure not to overcook them. I always cook a couple more noodles than I need since a couple seem to always break apart during the cooking process. Drain noodles then rinse with cold water.
To make filling, add beans, spinach, parmesan, garlic powder, dried herbs, and salt to a large bowl. Using a potato masher or fork, mash beans until they are mostly broken down. You don't want to see any whole beans. Carefully stir in milk.
To assemble, spread 1 1/2 cups of marinara on the bottom of your baking dish. Lay a lasagna noodle on your work surface and spread about 2 tablespoons of the bean mixture onto the noodle, leaving about a 1/2 inch at the top uncovered (see photo above). Sprinkle about a tablespoon of shreded mozzarella over the filling. Roll the lasagna noodle into a pinwheel and place seam-side down into the tomato sauce. Repeat with the remaining noodles.
Spoon the remaining marinara sauce over the lasagna roll-ups then sprinkle with the remaining cheese. Bake until cheese is golden brown and bubbly, 20 to 25 minutes. Serve warm.