Step 1

Heat 2 Tbsp. oil in a large cast-iron skillet over medium-high. Cook bread, tossing often and adding more oil if pan looks dry, until golden all over, about 4 minutes. Season croutons with salt and pepper; set aside.

Step 2

Cook peas in a large saucepan of boiling salted water until bright green and warmed through, about 3 minutes. Drain in a fine-mesh sieve and rinse under cold running water to stop cooking; set aside. Reserve saucepan.

Step 3

Combine shallot, thyme, vinegar, and red pepper flakes in reserved saucepan and cook over medium heat, stirring occasionally, until shallot is softened and vinegar is absorbed, about 4 minutes. Transfer to a medium bowl and add kombucha, mustard, and remaining 4 Tbsp. oil, whisking until emulsified. Season vinaigrette with salt.

Step 4

Toss fennel, Pecorino, watercress, green garlic, reserved croutons, and reserved peas in a large bowl to combine. Drizzle vinaigrette over and toss to coat. Season with salt and pepper and top with fennel fronds.