Melt butter in a large Dutch oven over medium-high heat. Add chopped onion and minced garlic, sauté for about 5 minutes until translucent.

Add half of the Cajun seasoning, stirring to coat the aromatics. Bloom for about 1 minute until aromatic.

Remove from heat, stir in chicken broth, diced tomatoes, and heavy cream. Return to medium heat, bring to a gentle boil, then simmer for 5 minutes.

Stir in dry Ditalini pasta and simmer for approximately 10 minutes until tender, stirring occasionally.

Season chicken with remaining Cajun seasoning, heat oil in a skillet, sear chicken for 3-5 minutes per side until golden and cooked through. Let rest before chopping.

Stir in grated Parmesan cheese until melted, fold in chopped chicken, simmer for another 2-3 minutes to combine flavors.

Ladle soup into bowls, garnish with sliced green onions, and serve immediately.