Season trout fillets with salt and pepper.
Fry trout skin-side down in hot oil for 5 minutes until crisp.
Turn off heat, flip fillets, and cook through on residual heat.
Blanch peas and carrots in boiling salted water for 2 minutes and refresh in cold water.
Blanch bacon lardons in boiling water for 1 minute and drain.
Sauté bacon in one tablespoon of butter until golden-brown.
Add vegetables and stock to the bacon, bring to boil, then simmer for 5 minutes.
Whisk in remaining cold butter cubes gradually until sauce thickens.
Stir in shredded lettuce and horseradish cream before removing from heat.
Serve trout atop the vegetable and sauce mixture.