Season tilapia fillets generously on all sides with Cajun seasoning. Preheat a large skillet over medium high heat.
Add oil and butter to pan; swirl and add fish fillets, browning on all sides, about 6 minutes total cooking time. Meanwhile, fry jalapeno slices in oil alongside. Remove both fish and jalapenos to serving plates. Top with fried jalapeno slices, sprinkle with lemon zest and squeeze with remaining lemon wedges, if desired.
As a suggestion, serve fillets with veggies and/or potatoes.