While mushrooms are cooking, heat canola oil over med-high heat in saute pan. Toss onion slices in flour, shaking to remove excess. Gently fry onions in canola oil until brown and crispy, remove to paper towels.
Just before serving, blanch green beans in salted boiling water for 3-4 minutes.
Spread generous spoonful of sauce on plates. Top with a bundle of green beans.
Sprinkle with crispy onions, shaved Parmesan, freshly cracked pepper and lemon wedges.
Serve with lemon wedge.
Recipe by Lemony Thyme at http://www.lemonythyme.com/green-bean-casserole-deconstructed/