Heat 1 tablespoon olive oil in a skillet over medium-high heat.
Season the chicken tenders lightly if desired, then sear in the hot skillet until both sides develop a light crust but the centers remain undercooked, about 1–2 minutes per side.
Transfer the seared chicken to the slow cooker in a single layer.
In a bowl, whisk together chopped lemongrass, 1/3 cup light coconut milk, 2 tablespoons fish sauce, 1 tablespoon lime juice, 1 tablespoon light soy sauce, 1 teaspoon chili garlic sauce (or sriracha), 1 tablespoon agave nectar (or 1 teaspoon coconut sugar), 1 teaspoon ground ginger, 1 teaspoon turmeric, and 2 minced garlic cloves until combined.
Pour the sauce over the chicken in the slow cooker, turning pieces to coat.
Cook on low for 3–4 hours or on high for 2–3 hours, until the chicken is cooked through and tender.
Serve the chicken with steamed vegetables and brown rice if desired.