MELT butter in a large non-stick frying pan over medium. Add frozen peas. Cook until peas are thawed, about 5 min. Transfer to a food processor. Whirl with avocado, feta, thyme, lemon zest and lemon juice until combined.
RETURN pan to stovetop and wipe clean with a paper towel. Crack eggs into pan. Cook, covered, until whites are no longer runny, 2 to 3 min.
SPREAD pea mixture on toasted sandwich bread. Top each with an egg. Sprinkle with fresh thyme. Serve immediately.