In a small bowl, combine mayonnaise, sweet relish, spicy mustard, dried thyme, and salt. Mix until smooth. Let sit for about 10 minutes.

In a large glass bowl or trifle dish, layer chopped iceberg lettuce at the bottom.

Sprinkle thinly sliced red onion over the iceberg lettuce.

Add a layer of chopped hard-boiled eggs on top of the red onion.

Sprinkle diced sweet peppers over the eggs.

Distribute thawed frozen peas across the sweet pepper layer.

Add a layer of shredded aged Irish cheddar on top.

Pour the prepared dressing evenly over the layered salad.

Let the salad chill in the refrigerator for 15-30 minutes before serving.

Gently toss the salad before serving to mix the layers while keeping the presentation intact.