Cook the onions, tomato paste, garlic, and thyme in 2 tbs vegetable oil in a large skillet over medium-high heat until softened about 8 to 10 minutes. Stir in flour and cook for a minute longer. Whisk in the chicken broth, scraping up any browned bits and stirring any lumps. Remove from heat and carefully transfer to slow cooker.
Stir the beef broth, portabellos, soy sauce, and bay leaves into the slow cooker with the onion mix. Pat the beef dry and season with salt and pepper. Add to the crock pot.
Arrange a sheet of heavy foil out and toss the veggies ( red potatoes, carrots, parsnips) with the rest of the veggie oil and toss to coat. Sprinkle with salt and wrap in the foil to create a packet. Gently lay the packet over the beef in the slow cooker. Cover and cook for 9 to 11 hours on low, until the beef falls apart with a fork.
Remove the foil pack from the cooker and let rest for 5 minutes. Using a slotted spoon, strain fat from the surface of the stew. Remove the bay leaves. Stir in the kale and cover for another 20 to 30 minutes.
Carefully transfer the veggies to the stew, (add additional broth if needed and heat through) stir and ladle into bowls.