Combine stock and chicken in a saucepan over medium heat; bring to a simmer. Cook 8 minutes or until done. Remove chicken with a slotted spoon; let stand 10 minutes. Shred chicken; set aside. Drain cooking liquid through a sieve over a bowl, reserving liquid; discard solids. Set aside 2 tablespoons liquid.
Return remaining cooking liquid to pan. Add salsa verde; bring to a boil. Cook until reduced to 1 cup (about 11 minutes). Reduce heat to low. Add cream cheese and cumin; stir with a whisk until smooth. Remove from heat; stir in chicken and 1/4 cup cilantro.
Heat a large skillet over medium heat. Add oil to pan; swirl to coat. Add onion, garlic, and mushrooms; sauté 8 minutes or until tender. Add kale, black pepper, and reserved 2 tablespoons cooking liquid. Cook 2 minutes or until kale wilts, stirring occasionally. Add kale mixture to chicken mixture. Divide chicken mixture evenly among tortillas. Top each with about 1 1/2 tablespoons cheese. Fold in edges of tortilla; roll up.
Heat a large nonstick skillet over medium-high heat. Coat all sides of each chimichanga evenly with cooking spray. Cook 6 to 8 minutes, turning to brown on all sides.
Combine avocado, milk, and 1 tablespoon lime juice in a mini food processor; process until smooth.
Combine tomatoes, remaining 2 tablespoons cilantro, and remaining 1 tablespoon lime juice in a bowl; toss. To serve, arrange 1 chimichanga on each of 8 plates. Top with 1 1/2 tablespoons avocado cream and about 1/4 cup tomato salad.