In a large bowl, combine ground chicken, ground beef, chopped onion, minced garlic, 1 teaspoon salt, 1/2 teaspoon black pepper, dried thyme, dried parsley, and ground nutmeg. Mix thoroughly until well combined.
In a separate bowl, whisk together the all-purpose flour, baking powder, and 1 teaspoon salt.
Add the cold unsalted butter pieces to the flour mixture. Use a pastry cutter or your fingers to cut the butter into the flour until the mixture resembles coarse crumbs.
Pour in the whole milk and stir until just combined to form a soft dough. Do not overmix.
Heat olive oil in a skillet over medium heat. Add the meat mixture and cook for 5-7 minutes, stirring occasionally, until the meat is browned and cooked through. Remove from heat.
In the crockpot, combine chicken broth, diced carrots, diced celery, and frozen peas. Stir to mix.
Drop the cooked meat mixture evenly into the crockpot broth and vegetables. Stir gently to combine.
Using a spoon, drop dumpling dough by tablespoonfuls evenly over the surface of the crockpot mixture.
Cover and cook on low for 6 hours, or until the dumplings are cooked through and the vegetables are tender.
Once cooked, serve warm directly from the crockpot.