We have featured several versions of shepherd's pie over the years, but packed with lentils, mushrooms and a savory spice mix, we think this vegetarian version will satisfy meat-eaters and vegetarians alike.
Turn on the oven's broiler and place an oven rack about 6" / 15cm under the heat source.
Place potatoes into a saucepan and cover with cold water and some salt. Cover and bring to a boil. Simmer uncovered for 12 to 15 minutes until potatoes can be easily pierced by a knife. Drain and let sit in a colander for ~5 minutes to let the steam escape (this creates creamier potatoes vs. liquidy potatoes).
While potatoes are cooking, heat a skillet or saute pan over medium-high heat. Add cooking oil and mushrooms to heated oil. Saute until mushrooms are deep golden brown, ~5 minutes. Add onions and white parts of green onions to hot oil. Saute until softened, 2 to 3 minutes. Add spice mix and saute until fragrant, ~1 minute more.
Add lentils and frozen vegetables and saute to heat through, ~1 minute. Stir in water, Worcestershire sauce and tomato paste.
Use a masher to mash steamed potatoes with sour cream, butter and some salt. Spoon over top of filling and spread to evenly cover.
Broil for 8 to 12 minutes, until the top is golden brown and crisp.
Whisk together vinegar, mustard and honey in a mixing bowl. Add olive oil while whisking. Add mixed greens, grapes and almonds to vinaigrette. Toss just before serving.
Sprinkle shepherd's pie with green parts of green onions. Enjoy with salad on the side.