Cook the lentils: In a saucepan, combine lentils with 4 cups water, bring to a boil, reduce heat to medium, and simmer for 20 to 25 minutes until tender (cook time will vary depending on the type of lentils you use—see package). Drain excess water.
Toast the walnuts: Preheat oven to 300°F. Add walnuts onto a rimmed baking sheet and toast for 10 to 13 minutes, watching closely, until lightly golden and fragrant. Set aside to cool for a few minutes.
Make the salsa: Combine all salsa ingredients in a bowl, and toss well.
Make the guacamole: Combine all guacamole ingredients in a bowl and mash with a fork until well combined. Leave a little chunky.
Make the Cashew Sour Cream: Drain the cashews. Then, place all cashew sour cream ingredients in a bullet blender, and blend on high until smooth. You can add additional water to thin it out as desired.
Prepare the taco meat: Add cooked lentils and all the toasted walnuts into a large bowl, along with the spices salt, and oil. Mix and mash with a fork, until thoroughly combined, add in a tablespoon of water at a time until combined.
Assemble: Add a large lettuce leaf onto a plate, top with taco meat, radish salsa, guacamole, and a drizzle of cashew sour cream.