Working in batches, toast pumpkin seeds and sunflower seeds in a dry skillet over low heat. Stir frequently to prevent burning and remove from heat when fragrant.
Combine cooled pumpkin seeds, sunflower seeds, and ground flaxseed in a food processor and process for a minute.
With the food processor running, slowly drizzle in ¼ cup oil. Continue processing until mixture is smooth and creamy, about 5 minutes. You may need to occasionally turn off the food processor and scrape it down with a spatula.
Taste and add salt and/or sweetener, if desired. (Add just a small amount at a time and taste frequently.)
If mixture is too dry, continue to add a little more oil, processing until desired consistency is reached.
Transfer to an airtight container and store in refrigerator up to 2 weeks.
