For the macadamia and dill pesto, whiz all ingredients in a food processor. Season and chill.
Place potatoes in a saucepan and cover with cold water. Bring to the boil. Reduce heat to medium-low and cook for 15 minutes or until tender. Drain and refresh. Cut into large pieces and place in a bowl.
Heat oil in a frypan over medium heat. Add breadcrumbs and cook, stirring, for 8 minutes or until crisp.
Remove from heat. Add lemon zest and freshly ground black pepper.
Place pancetta in a non-stick frypan over medium heat and cook, turning once, for 6-7 minutes or until crisp. Cool, then roughly crumble.
Add pesto to potato and toss to coat. Transfer to a serving bowl and scatter with breadcrumbs, pancetta and watercress.