Step 1

Preheat oven to 375°F. Line a baking sheet with foil. Set 6 large ramekins on the baking sheet. Coat lightly with cooking spray.

Step 2

Heat oil in a large heavy skillet over medium-high heat. Add onion, mushrooms, oregano or marjoram and ½ teaspoon salt, and cook, stirring occasionally until the vegetables start to brown, about 10 minutes. Add lentils, spinach and tomatoes and bring to a simmer. Remove from the heat and divide among the prepared ramekins.

Step 3

Meanwhile, bring 1 inch of water to a boil in a large saucepan fitted with a steamer attachment. Add squash to the steamer, cover and cook until the squash is tender with pierced with a fork, 12 to 14 minutes. Empty squash into food processor. Add butter, yogurt and the remaining ½ teaspoon salt. Puree until smooth, scraping the sides of the processor as necessary. Divide the squash over the lentil mixture in the ramekins.

Step 4

Top the shepherd’s pie with cheese, dividing evenly. Bake until the pies are bubbling, and the cheese is melted, 10 to 15 minutes. Cool slightly before serving.