Sauté sliced mushrooms and shallot in butter and olive oil over med-low until mushrooms have released all their liquid, about 10 minutes. Add thyme leaves, tarragon, and garlic and sauté 2 minutes more. Add wine and stir deglazing pan for 1 minute. Sprinkle flour over mushroom mixture. Add heavy cream and continue cooking 3-4 minutes until sauce thickens. Season with salt & generous amount of pepper to taste.
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.