Uy, I totally get it, my son was exactly the same, puro sauce and easy stuff lang! What worked for us is mixing the gulay finely into the sabaw ng sinigang or nilaga niya na, so hindi siya nakikita but getting the nutrients pa rin, tapos gradually I started leaving slightly bigger pieces so bumitaw siya sa texture. One of my mum friends swears by cooking the chicken super soft and shredding it into his noodles or adobo sauce kaya parang part na lang niya ng comfort food, not a separate thing na "healthy" looking, kids are weird that way, basta parang same meal lang, kumakain na sila! Try rin mixing finely minced fish sa sarsa ng adobo para sa umami flavor na gusto niya, madali gawin at hindi mapapansin. Patience lang talaga, eventually they expand their palate, pero starting from what they love helps a lot.