Chop bacon and cook in a large Dutch oven over medium heat until crispy, 3 to 4 minutes. Drain on paper towels.

Add oil to the pan. Add celery, leek, salt and pepper and cook until the vegetables just begin to soften, about 2 minutes. Add broth, potatoes and corn. Bring to a gentle simmer. Cook until the potatoes are just tender and the corn is cooked through, about 8 minutes. Stir in tilapia and thyme; return to a gentle simmer. Cook until the tilapia is cooked through, about 4 minutes more. Remove from the heat.

Stir in half-and-half, lemon juice and the reserved bacon. Garnish with chives, if using.