Peel, seed and chop squash into 1" chunks, discarding seeds and fibers, you should have about 4 cups.
In a medium saucepan, heat vegetable oil over medium-high heat until a bit of garlic sizzles at once. Add remaining garlic and toss well. Cook, until fragrant, about 1 minute.
Add pumpkin, and toss well. Cook, tossing occasionally, until shiny with oil and beginning to soften, about 1 minute more. Add stock, fish sauce, sugar, sugar, salt and pepper. Stir well and bring to a boil.
Reduce heat and cook at a lively simmer until pumpkin is very tender and has a small about of creamy sauce, about 20 minutes. Remove from heat and serve hot, warm or room temperature.