Peel and dice potatoes into small, even cubes. Chop onion finely and mince garlic cloves. If chicken isn't cooked, poach or roast it, then shred into bite-sized pieces.
Heat olive oil in a large pot over medium heat. Add chopped onion and cook until translucent and fragrant, about 4-5 minutes. Stir in minced garlic and cook for 1-2 minutes, avoiding browning.
Add diced potatoes and corn kernels to the pot. Pour in chicken broth and sprinkle in dried thyme, salt, and pepper. Stir to combine.
Bring mixture to a boil, then reduce heat and simmer gently for 15-20 minutes or until potatoes are fork-tender.
Add shredded chicken to the pot, stirring gently to warm through. Pour in heavy cream, stirring until chowder is creamy and combined. Simmer for another 5 minutes.
Taste chowder and adjust seasoning with more salt or pepper as needed. For thicker chowder, simmer uncovered longer to reduce liquid.
Ladle chowder into bowls and garnish with chopped green onions. Serve with crusty bread or salad for a complete meal.
