Demo of using @AuraEnabled without getter/setter in both Aura and LWC (SFSE: 292183)

q292183.app

<aura:application controller="q292183">
    <aura:handler name="init" value="{!this}" action="{!c.init}" />
    <aura:attribute name="data" type="Map" />
    {!v.data.a} {!v.data.b} {!v.data.c}
    <hr />
    <c:q292183lwc />
</aura:application>

q292183.apxc

public class q292183 {
    public class Response {
        @AuraEnabled public String a, b, c;
    }
    @AuraEnabled(cacheable=true) public static Response getData() {
        Response res = new Response();
        res.a = 'Hello';
        res.b = 'World';
        res.c = 'Everyone';
        return res;
    }
}

q292183Controller.js

({
	init : function(component, event, helper) {
		var action = component.get("c.getData");
        action.setCallback(
            this, 
            response => component.set("v.data", response.getReturnValue())
        );
        $A.enqueueAction(action);
	}
})

q292183lwc.html

<template>
    <template if:true={data}>
    {data.a} {data.b} {data.c}
    </template>
    <template if:true={error}>
        {error}
    </template>
</template>

q292183lwc.js

import { LightningElement, wire, track } from 'lwc';
import getData from '@salesforce/apex/Q292183.getData';

export default class Q292183lwc extends LightningElement {
    @track data;
    @track error;
    @wire(getData, {}) 
    result({data, error}) {
        this.data = data;
        this.error = error;
    }
}

q292183lwc.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <apiVersion>47.0</apiVersion>
    <isExposed>false</isExposed>
</LightningComponentBundle>

@brianmfear, mine is failing as an Apex type as an input parameter to an Apex method, not the return. But now that I'm saying that, I wonder how common is that really? Adding 2-3 params isn't a big deal. But you only get one object to pass back. So probably much more prevalent to pass back an Apex type than to use as input.