In a food-processor, pulse and grind the chicken thighs and chicken liver until smoothly ground/pureed (if you have a small food-processor, you may do this in 2 batches). Make sure there are no large chunks left when you do this, and transfer the ground meat into a stand-mixer bowl. Then add the granny smith apple and carrot in the food-processor (no need to wash), pulse until finely minced, and transfer to the stand-mixer bowl as well. Grind the flaxseeds with 1/2 cup of rolled oats in a spice-grinder. Rinse the frozen peas through a sieve to make sure they are separated WITHOUT any ice-cubes attached, dry thoroughly on a kitchen towel. Add everything along with the remaining 1/2 cup of rolled oats, sesame oil, safflower oil and salt to the stand-mixer bowl.
With a stand-mixer, beat the mixture with a paddle-attachment on high speed for about 5 min, until thick and sticky. What this does is it binds the excess water in the mixture with protein, and gives you springy meatballs that won’t release water during baking. You can do this by hand with a wooden spoon, but expect really sore muscles. If you want to skip this step, be warned that you might get watery meatballs in the oven.
Line baking sheets with parchment paper, and make mini meatballs the size of a large melon-baller, with 1? (3 cm) space in between. Place the baking sheet on the middle-upper rack in the oven, about 3 1/2? (9 cm) below the broiler. Bake for 15 min, but remember to shake the baking sheet every 5 min in between to roll the meatballs around for even browning. Prepare another sheet of meatballs while the first batch is baking, then after 15 min, move the first batch to the lower rack in the oven for another 5 min to finish cooking, and place the second batch on the middle-upper rack to brown. Repeat the same process with every batch.
After each batch has been baked on the middle-upper rack for 15 min, then the lower rack for another 5 min, you can remove it from the oven and let then cool on a cooling-rack.
Store them in an air-tight container in the fridge for up to 5 days, or freeze them for up to 2 months. Reheat in the microwave to bring them back to room-temperature (but not hot!) before giving them to some seriously wagging tails.