Move your oven rack to the top shelf, as close to the broiler as possible. Set your oven to broil and line up the bell peppers on a baking tray. Broil until the tops of the peppers are blackened, about 5 minutes, turn the peppers over and broil for another 5 minutes. Remove from the oven and set aside to cool.
While the peppers are broiling, heat the avocado oil in a large pot or Dutch oven over medium-high heat. Add in the onion, celery, and carrot. Sautee until softened, about 10 minutes. Add in the garlic, salt, thyme, red pepper flakes, and oregano and sauté for another 2 minutes. Transfer the contents of the pot to a blender.
Once the bell peppers are cool enough to tough, use your hands to peel of the skin and remove the top and the seeds. Place in the blender along with the vegetable broth. Blend until smooth.
Transfer the blended soup back to the pot and heat over medium to warm through, about 5 minutes. Serve.