Heat oil in a large skillet over medium-high heat for two minutes. You'll know it's ready when a drop of water sizzles on contact—this matters because you're about to unlock flavor. Toast your curry powder and cumin together for just sixty seconds, stirring constantly. I learned this the hard way after burning a batch; the goal is fragrant, not dark brown.
Add your diced onion to the toasted spices and cook for three minutes until softened and fragrant. Stir in minced garlic and fresh ginger, cooking another minute. This step builds the foundation of your slow cooker chicken curry crowd recipe—rushing it results in raw garlic taste that never disappears.
Transfer the onion mixture to your slow cooker along with chicken thighs, arranging them so they're mostly covered by liquid. Pour in coconut milk, chicken broth, diced tomatoes with their juice, brown sugar, salt, and black pepper. Stir gently to combine without breaking apart the chicken.
Cover and cook on low for eight hours or high for four hours. The longer cook time is worth the wait because it allows the slow cooker chicken curry crowd recipe to develop deeper flavors that quick versions simply can't match. I check at the six-hour mark—chicken should shred easily with a fork.
About thirty minutes before serving, taste and adjust salt. Stir in lemon juice and fresh cilantro. The lemon brightens the sauce right before the table gets it, which is why timing matters here.