PREP: Measure the lentils and pick over to remove debris or shriveled lentils; add to a fine-mesh sieve, thoroughly rinse with cool water, and set aside. Prep the veggies: finely dice the onion and thinly slice carrots (cut thick carrots in half lengthwise first and then thinly slice (to create half moons), dice potato (no need to peel if using Yukon gold) into small 1/2 inch pieces. Cut carrot and potato small so they'll cook in the right amount of time. Finely mince the garlic cloves and the ginger.
SAUTE: Measure the 3 tablespoons butter or coconut oil when solid and heat in a large cast iron pot to medium-high heat. Add in onion, carrots, and potatoes. Saute for 7-9 minutes, stirring frequently, until golden. Add in the garlic and ginger. Cook for another 1-2 minutes, stirring constantly. Nothing should be overly browning or burning; if so, turn down the heat. If you aren't using a cast iron pot, cook times will be longer (cast iron holds heat better). While everything is cooking, measure out the spices.
SPICES AND TOMATOES: To the pot, add all the spices. Season with salt and pepper; I add 1 and 1/4 teaspoon fine sea salt and 1/2 teaspoon ground pepper. Cook, stirring constantly, for 1-2 minutes or until very fragrant. Add in the (undrained) tomatoes, reduce the heat to medium, stir and cook for 2-3 minutes, scraping the bottom of the pot to release any browned bits.
LENTILS AND LIQUIDS: Vigorously shake the can of coconut milk. Open and remove 1/4 cup and set aside for later. Add vegetable stock, lentils, and remaining coconut milk to the soup. Bring to a boil, reduce heat to low, and gently simmer, uncovered, for 15-20 minutes or until lentils and veggies are tender. Stir occasionally. Red lentils can get mushy if over-cooked so check at 15 minutes. If soup thickens too much, add a splash more broth/stock (we do like this soup pretty thick!) and if it's too thin (or lentils aren't tender), increase the heat a bit to simmer at a slightly higher heat.
FINISHING: Remove from heat. Stir in the frozen peas and optional 1/3 cup finely chopped cilantro. Stir in the zest and juice of a lemon. Taste and adjust any seasonings; flavors should sing, so add extra salt, pepper, or lemon juice if needed.
SERVE: Ladle into bowls and serve with lemon wedges. (We love lots of lemon in this soup!) Use a spoon to drizzle reserved 1/4 cup coconut milk onto the tops of bowls and sprinkle in toasted coconut flakes if desired. Enjoy!