Heat the oil over medium heat and add the onion. Cook for a couple minutes until onion begins to become tender. Crumble into the pan the chicken sausage. Cook until onion is translucent and sausage is browned. Add salsa, corn and cumin. Simmer over low to combine flavors and season to taste with salt and pepper. Stir in cilantro then 2 tablespoon of the manchego cheese.
Lay the poblano flat then cut a T-shaped slit into the top of the poblano. Using your fingers, pry the slit apart and remove the seeds and membrane.
Stuff the sausage mixture into the poblano peppers. Top each poblano with 1 tablespoon of the remaining manchego.
Bake approximately 25-35 minutes, until the poblano is tender and cheese is melted.