There are four changes from the side that beat Scotland 43-15 in the final game of the Six Nations championship in March.
Wing Dafydd Howells returns in place of Joshua Adams, Ethan Lewis gets the nod at hooker, Rory Thornton comes in to the second row instead of Ben Roach and Scott Matthews starts in the back row over Will Boyde, with James Benjamin moving back to his more usual position of No 8. Scrum half Luc Jones, and flanker Olly Cracknell, who got their first Wales Under 20 starts in that win over Scotland, have retained their jerseys for this game.
Hayward said, "We believe this is our strongest team at the moment. Training has gone particularly well in the last month, with conditioning playing a key part and the warm-up game against Scotland before we left Wales was very useful.
"Luc played and trained well while Tom Williams was out injured and has taken his chances, while Olly brings a physical presence that could help us against Fiji. Rory Thornton has also impressed in training, especially with his line-out presence. The hooking decision was arguably the most difficult one to make with three very strong candidates and Ethan just edging it.
"It's crucial we deliver a disciplined, tactical performance on Monday in order to build momentum for the rest of the tournament."
Wales reached the final of last season's tournament and the last four in South Africa two years ago, so expectations are understandably high but Hayward is realistic about his squad's targets for the competition.
"We have three physically demanding games in nine days. After the challenge of Fiji, we have Ireland and then Grand Slam champions France but if we can win those games and get through to the semi-finals, we showed last year in beating South Africa that anything can happen."
Wales team v Fiji: Ashley Evans (Ospreys); Tyler Morgan (Dragons), Steffan Hughes (capt, Scarlets), Jack Dixon (Dragons), Dafydd Howells (Ospreys); Angus O'Brien (Dragons), Luc Jones (Dragons); Nicky Smith (Ospreys), Ethan Lewis (Blues), Nicky Thomas (Ospreys), Joe Davies (Dragons), Rory Thornton (Ospreys), Olly Cracknell (RGC), Scott Matthews (Dragons), James Benjamin (Dragons)
Replacements: Elliot Dee (Dragons), Callum Lewis (Blues), Benjamin Leung (Scarlets), Ben Roach (Blues), Will Boyde (Carmarthen), Tom Williams (Blues), Ethan Davies (Dragons), Joshua Adams (Scarlets)
Junior World Championship 2014
Wales Under 20 Pool fixtures:
Monday 2 June: Wales v Fiji, ECOLight Stadium, Pukekohe, 15.35 local time (as live, 9.30pm S4C)
Friday 6 June: Wales v Ireland, ECOLight Stadium, Pukekohe, 17.35 local time (live on Sky, extended highlights 9.30pm S4C)
Tuesday 10 June: Wales v France, QBE Stadium, Auckland, 15.35 local time (as live, 10pm, S4C)