Preheat oven to 375°F (190°C). Line a baking sheet with foil or parchment paper (for easy clean-up) & place a greased wire rack on the baking sheet.
Arrange chicken on the wire rack. Roast for 45 to 50 minutes or until cooked when a small knife inserted into a chicken thigh produces clear liquid. Let stand until cool enough to handle. Remove & discard skin. Remove chicken from each bone. Set bones aside in a re-sealable bag to freeze for bone broth (optional). They can be frozen up to 3 months. I usually wait until I have about 12 or more to make a big pot of broth. Cut the chicken into pieces – this will depend on the size of your dog & its teeth; I have a xoloitzucinintle (Mexican hairless) & he doesn’t have many teeth so his food is diced.
While the chicken is cooking, heat the oil in a large frying pan over medium-high heat. Add beef & cook for 5 to 7minutes, or until beef is browned, breaking up large lumps with a spoon. Remove beef to a large bowl using a slotted spoon.
Add squash to the same pan (don't clean it). Add just enough water to almost cover the squash. Cook, stirring occasionally & scraping any bits of stuck on beef off the bottom of the pan. Cook squash, partially covered, for 5 to 7 minutes or until tender but not mushy. Remove squash to the same bowl as the beef using a slotted spoon.
Cook the beans in any residual water left from cooking the squash, if necessary, add a little more water. Cook 2 to 3 minutes or until softened. Remove beans to the same bowl using a slotted spoon.
Add spinach & cook for about 30 seconds until just wilted; remove to the same bowl using a slotted spoon.
Heat 2 cups of water in the same pan (no need to clean it). Add oats & cook, stirring, for 3 to 5 minutes, or until oats are softened. Scrape the oats into the bowl with the other ingredients. Add the chopped chicken & stir until all ingredients are combined.
Let the mixture cool for about 10 minutes if it’s still hot, before spooning it into containers, re-sealable bags or jars. Makes about 10 cups.