Meatballs:: In a bowl, whisk together egg, bread crumbs, 1/4 cup water, oregano, salt and pepper; mix in beef.
Shape by rounded teaspoonfuls into balls. Bake on a foil-lined rimmed baking sheet in a 400°F (200°C) oven until no longer pink inside, about 12 minutes.
Tomato Sauce: Meanwhile, in a large saucepan, heat oil over medium heat; fry onions, garlic, carrot, celery, herb seasoning, and salt and pepper, stirring occasionally, until the onion is softened, about 5 minutes.
Add the tomato paste and tomatoes (presumably with the juice), breaking up with potato masher or some such thing, bring to a boil. Reduce heat and simmer for 45 minutes.
Add the meatballs; simmer until a spoon scraped across bottom of pan leaves a gap that fills in slowly, about 10 minutes.
Bechamel Sauce: Meanwhile, in separate saucepan, melt the butter over medium heat; whisk in flour and cook, whisking, for 1 minute.
Add the milk 1/2 cup at a time, whisking constantly. Keep whisking and cooking until bubbly and thickened, about 5 minutes. Whisk in ricotta, Parmesan, salt, pepper and nutmeg.
In large pot of boiling salted water, cook lasagna noodles until almost tender, 6 to 8 minutes. Drain and chill in cold water; arrange in single layer on a damp tea towel.
Without picking up any meatballs, spoon 1 cup of the tomato sauce into a 13- x 9-inch (3 L) glass baking dish. Top with one-third of the noodles; spread with one-third of the remaining sauce and meatballs, then half of the bechamel sauce. Starting with the noodles, repeat the layers once.
Top with remaining noodles; spread with the remaining meatball sauce. Sprinkle with Fontina and Parmesan cheeses.
Cover with foil; bake in 375°F (190°C) oven for 20 minutes. Uncover and bake until bubbly and golden brown, 20 to 25 minutes. Let stand for 10 minutes.