Mix all the spices together in a small bowl. Add the spice blend and all ingredients to the slow cooker. Mix until ingredients are evenly distributed, then set the slow cooker to cook on High for 4 hours.
While the tikka masala is slow cooking, place cashews in a bowl of hot water and soak for at least one hour. Place the cashews in a high speed blender with 1.5 cups water and blend until smooth and creamy.
Once the slow cooker is done, add the cashew cream and lemon juice and stir until well combined. If needed, add salt to taste.
Serve immediately with rice of choice or naan. Store in the refrigerator and eat within 4 days, or freeze up to 4 months.