In a small saucepan, bring the water and milk to a gentle boil over medium heat.
Whisk in the stone-ground grits and sea salt, then reduce heat to low, cover, and simmer for 15-20 minutes, whisking occasionally until creamy.
While the grits are simmering, heat the ghee in a large skillet over medium-high heat.
Add the diced yellow onion and bell pepper to the skillet and sauté for 3-4 minutes until the vegetables are softened and fragrant.
Toss the raw shrimp with Cajun seasoning and black pepper in a small bowl until evenly coated.
Add the seasoned shrimp and minced garlic to the skillet, searing for 2-3 minutes per side until the shrimp are pink and opaque.
Once the grits are tender, remove from heat and stir in the plain Greek yogurt to achieve a silky texture.
Divide the creamy grits into bowls and top with the sautéed Cajun shrimp and vegetable mixture.
Garnish with freshly sliced green onions and serve immediately.