Preheat oven to 425 degrees Fahrenheit.
On 2 parchment lined baking sheets, toss cauliflower with about a tablespoon of oil and a pink of salt. Bake for 30 minutes.
Meanwhile, in a large stockpot over medium heat, add 2 tablespoons of oil and the onion and garlic. Cook for 7 minutes, stirring occasionally, before adding the peas and broth. Cook another 7 minutes.
When the cauliflower is done, carefully add it to a blender, along with the onion/pea/broth mixture, dill, baby spinach, lemon, and salt. You may have to do this in two batches, in which case, put half of everything into the blender at a time. When blending hot liquids, always remove the center piece and hold a dish towel over the opening when blending, to let steam out. Blend until smooth.
Pour into bowls, or if batch cooking for the week, four pint-sized mason jars. If not eating right away, cover and refrigerate.